prop size help

[jakedaawg]

Need to prop a couple pontoon boats. Need some starting pitches and diameters.

Boat 1: 20' Bennington pontoon w/ 70hp evinrude 2-stroke. Was thinking about a 13 Pitch

Boat 2: 25' lund pontoon w/ 40hp evinrude 2-stroke. Was thinking about an 11 pitch

If anyone has a pontoon with similiar size boat and engine maybe you could let me know what you have on. The fewer trips to the prop shop the better.

I don't have props for either boat so I cant just do the math.

 

[steelespike]

Re: prop size help

What year are the motors?I think the first year for the 70 was 74 first years for the 40 was 60?
Do you know the gear ratios?
Depending on the year they may have the same gear ratios.
I like to err on the low side I think a 10" for the 40 hp and an 11" for the 70.
These would be considered a starting point Hopefully if wrong they are too light.
If too light you can still use them by watching the rpm.If too heavy you shouldn't use them for an extended time.
Wouldn't it make sense to put the 70 on the big boat?

 

[jakedaawg]

Re: prop size help

Thanks, these are two seperately owned vessels, cant switch engines. A bunch of props were stolen at the storage lot. The 40 is an EC so '98. The 70 is an SS so 2000. I dont know the gear ratios was just hoping someone had something similiar so as to save a little time.
Thanks again for the reply. I am only ask to borrow two props at a time from the prop shop so the closer I come the quicker it is.

 

[steelespike]

Re: prop size help

My limited info indicate the 70 is a 2.23 ratio and the 40 is 2.42.
Then you have to hope you can get a accurate rpm and gps speed.

 

[BobGinCO]

Re: prop size help

A bunch of props were stolen at the storage lot.

That is a true tragedy!